Photographic diffusion transfer process



United States Patent Ofifice 3,062,643 PHOTOGRAPHEC DlFFUSlON TRANSFERPROCESS? Roy C. Bloom and Frederick A. Pomeroy, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey No Drawing. Filed May 22, 1959, Ser. No. 814,971

3 Claims. ((31. 9629) This invention relates to photography and moreparticularly to a silver halide diffusion transfer process in the art ofphotography.

In the Yackel, Yutzy, Foster and Rasch US. patent application Serial No.586,705, filed May 23, 1956, is described a diffusion transfer processemploying an integral photosensitive element comprising a silverprecipitating stratum such as colloidal silver on a support and adheredto this stratum an emulsion layer containing silver halide uniformlydispersed in alkali-soluble acidinsoluble carboxylated cellulosederivative such as an alkali-soluble acid-insoluble dibasic acid esterof a cellulose ethyl ether or an alkali-soluble acid-insoluble dibasicacid ester of a cellulose acetate. After exposure of the photosensitiveelement, the latent image therein is developed with a silver halidedeveloping composition containing a silver halide solvent, thus forminga negative silver image in the emulsion layer together with an imagewisedistribution of undeveloped silver halide which diffuses imagewise tothe silver precipitating stratum, in the form of a silver complex withthe silver halide solvent, to form a positive silver-containing image onthe precipitating stratum. Thereafter, the emulsion layer is removedfrom the silver precipitating stratum leaving a readily visible positivesilver-containing image thereon.

As is well known, the tone of the silver image obtained in the silverhalide diifusion transfer processes is characteristically warm in tonerather than being cold or neutral toned as is desirable and in the aboveprocess the inventors recommend that certain sulfur-containing compoundsbe present during processing to obtain cold-toned images.

We have discovered that a pronounced improvement in image tone in thedescribed process may be effected by use of common inorganic chemicals.The means we employ to produce the cold-toned images comprises the usein the silver halide developing composition of a mixture of a quaternaryammonium salt, a 3-pyrazolidone developing agent or a lowermonoalkyl-p-aminophenol developing agent, e.g. monomethyl-p-aminophenolsulfate, a hydroquinone developing agent, a sulfite such as an alkalimetal or amine sulfite, an alkaline material such as sodium carbonate,triosodium phosphate or sodium metaborate, a silver halide solvent, andpotassium chloride. The image tone is decidedly neutral when theseingredients are present in the developer composition but when, forexample, potassium chloride is not present in the composition, abrown-toned silver image is obtained whether or not the quaternaryammonium salt is present. Substitution of sodium chloride for potassiumchloride in the formula results in the production of a warm-toned silverimage. A specific effect obtained by use of trisodium phosphate as thesource of alkali is to prevent the formation of bronze or metallicluster-toned images characterized by the use of other alkaline materialssuch as sodium carbonate.

The process of our invention is illustrated by the following examples:

Example 1 A percent gelatin solution (250 cc.) was diluted with 750 cc.of water and then 2.5 cc. of l-N-sodium sul' 3,062,643 Patented Nov. 6,1962 fide were added to the solution. 250 cc. of water containing 26 cc.of 1 N zinc nitrate were added slowly to the sulfide solution through ajet, resulting in the formation of a colloidal dispersion of zincsulfide. To this dispersion were added 10 liters of a 3% gelatinsolution, 300 cc. of a 7.6% saponin solution and 134 cc. of a 10%formaldehyde solution. The mixture was dispersed at 40 C. and thencoated on a photographic paper support at a coverage of 2 lb. ofsolution per sq. ft. of coated surface and dried, forming the silverprecipitating layer.

Over the silver precipitating layer was coated a 1% aqueous solution ofthe sodium salt (or other alkali metal metal salt) of cellulose etherphthalate (an ethyl cellulose containing 45.8% ethoxyl phthalated to22.7 phthalyl) at a coverage of 0.15 lb. per sq. ft.

A low gelatin cellulose ether phthalate emulsion as dis closed by Yackelet al. above was coated over the cellulose ether phthalate interlayer ata coverage of 600 sq. ft. per mole of silver halide and dried in theconventional manner. After exposure, the element was developed for about1 minute in the following developer composition at 70 C.:

1-phenyl-3-pyrazolidone 0.8 Hydroquinone 5.5 Sodium sulfite (anhy.) 25.0Sodium carbonate (anhy.) 32.0 Sodium thiosulfate-5H O 10.02-,8-phenethylisoquinolinium bromide 0.15 Potassium chloride 16.0Potassium bromide 0.05

Water to 1.0 l.

The processed paper was washed for 20-30 seconds in cool water (30 C.)to remove the emulsion layer, leaving only the transferred positiveimage in the silver precipitating layer. The material was then rinsed ina 5 percent acetic acid stop bath for 5 seconds and dried. During thementioned development step, a negative silver image was formed in theemulsion layer and the residual undeveloped silver halide was dissolvedby the thiosulfate and transferred in the form of the complex silverthiosulfate salt to the zinc sulfide reception layer and was thereconverted to a silver-containing image which appeared as a neutral-toneimage when the overlying emulsion was removed.

Example 2 The process of Example 1 was carried out in the same mannerexcept using the following developer composition in which trisodiumphosphate replaced sodium carbonate as the alkaline component:

1-phenyl-3-pyrazolidone 1.6 Hydroquinone 1 1.0 Sodium sulfite (anhy.)50.0 Trisodium phosphate (hydrated) 100.0 Potassium bromide 0.5Potassium chloride 16.0 2-{3phenethylisoquinolinium bromide 0.3 Sodiumthiosu1fate-5H O 20.0

Water to 1.0 l.

The result was to obtain a print on the silver precipitating layer whichwas neutral in tone.

When the developer compositions of the above examples were used forprocessing a variety of silver halide emulsions similar to that ofExample 1, differing in their mode of preparation, optical and chemicalsensitizing and other factors, it was found that the formula of Example2 containing trisodium phosphate in most cases yielded neutraltonedimages while some emulsions showed a tendency aoeaeas to yield asomewhat warmer-toned image with the formula of Example 1.

The ingredients of the above formulas may be present in a fairly widerange of concentration and still favorable silver image tone will beobtained in the process. Useful results are obtainable by use of thefollowing amounts per liter of solution, from about 0.05 to 0.3 gram ofthe quaternary ammonium salt, about 50 to 100 grams of trisodiumphosphate, about 12 to 20 grams of potassium chloride and about 30 to 60grams of sodium sulfite. Lower concentrations of sodium sulfite tend toreduce the image density and higher concentrations of sodium sulfitepromote warm-toned image formation. As mentioned, if potassium chlorideis replaced by sodium chloride, :1 warm-toned image results in theprocess.

The silver halide solvent of the developer composition is not especiallycritical and can be an alkali metal or ammonium thiosulfate, sodiumthiocyanate, etc.

The 3-pyrazolidone silver halide developing agents useful in thesolutions include 1-phenyl-3-pyrazolidone,lphenyl-4,4-dimethyl-3pyrazolidone and other 3-pyrazoliclones describedin the James et al. U.S. Patent 2,751,300, granted June 19, 1956. Thehydroquinone useful in the developing solution include hydroquinoneitself, halogenated hydroquinones such as chloro and bromohydroquinones,dichloro and dibromohydroquinones and toluhydroquinone; etc.

Additional quaternary ammonium salts which may be used in the aboveformulas in place of the quaternary ammonium salt given are thosedisclosed in the Tregillus et al. U.S. Patent application Serial No.724,828, filed March 31, 1958, including the following of which thecyclammonium quaternary ammonium salts are particularly useful.

Tetradecamethylene-bis (pyridinium perchlorate)a-Dimethyldithiocarbamatoethyl-N methyl pyridinium-ptoluene sulfonateDecamethylene-u,w bis (oxymethyl pyridinium perchlorate)3,6,9,12,15,18,21,24-ctahexacosane 1,26 bis(-ethyl-2- methyl pyridiniummethane sulfonate) 2-,8-phenethylisoquinolinium bromide1-,8-phenethylquinolinium bromide3,l4-dioxahexadecane-1,16-bis-(pyridinium methane sulfonate)l-methyl-2-nonanoyl pyridinium-p-toluene sulfonateHeptoxymethyl-ZA,6-trimethyl pyridinium chloride Tetradecamethylenebis(trimethyl ammonium perchlorate) 3-methyl-2-B-phenethylisoquinolinium bromide l-fi-phenethyl-a-picolinium bromide4,4,10,10-tetraoxo 4,10 dithiatridecane-bis-(pyridinium perchlorate) Theuseful quaternary ammonium compounds are characterized by having a chainof at least 7 atoms attached to the onium radical. Similar oniumcompounds containing short chains such as tetramethylammonium hydroxide,halides, perchlorates and other salts thereof, are not useful in theprocesses of our invention.

As mentioned above, the photosensitive elements useful in the processesof our invention include a silver halide emulsion layer, the colloidvehicle of which is an alkalisoluble acid-insoluble carboxylatedcellulose derivative such as the alkali-soluble acid-insoluble dibasicacid halfesters of cellulose ethyl ethers e.g. the cellulose etherphthalates or the alkali-soluble acid-insoluble dibasic acid half-estersof cellulose acetate e.g. cellulose acetate phthalates. When thesematerial are employed as vehicles for emulsion superposed on silverprecipitating layers of a different solubility, the emulsion is quicklyremoved with aqueous alkaline solutions; that is, after the developmentstep is complete and the soluble silver complex has migrated imagewiseto the silver precipitating layer, the carbokylated cellulose derivativeis present as the alkali metal, ammonium, or amine salt, which is highlysoluble in water although not soluble in the alkaline developer becauseof its high salt content. Therefore, When the developed element issubsequently washed with Water, the emulsion disintegrates withsurprising rapidity and the positive image which remains on the silverprecipitating layer is quickly freed of any contaminating materials by abrief wash with water.

The acid-insoluble characteristic of the above carboxylated cellulosederivatives is likewise important due to the fact that the coating ofthese derivatives is greatly facilitated by this characteristic. Thatis, since the carboxylated cellulose derivatives are insoluble in acid,coatings thereof may be caused to quickly set during high speed coatingoperations by applying the coating to an acidic surface which in thepresent invention takes the form of a support having on its surface orin the silver precipitating layer an acidic material such as an organicacid, e.g., citric acid. The acid causes the carboxylated cellulosederivative coating to set, and subsequent drying operations can becarried out without undue distortion of the coating. Materials such asmethyl cellulose being soluble in both aqueous alkali and aqueous aciddo not possess the mentioned characteristic.

In a similar manner, the carboxylated cellulose derivative emulsions maybe coated upon a surface containing metal salts such as calcium acetate,aluminum nitrate, cadmium acetate, magnesium chloride and nickel acetatewith the result that the emulsion will readily set up and dry withoutdistortion. The use of acids in the sensitive element is thus avoided.Yackel et al. above show that other organic colloids are not as usefulas the carboxylated cellulose derivatives as the colloid vehicle for theemulsions and the same applies to the processes of our invention.

The silver precipitating layer or stratum referred to herein is aWater-permeable organic colloid layer containing a silver precipitatingagent, that is, an agent capable of yielding with silver ion adark-colored argental or silvercontaining substance, when dissolvedsilver salts from the emulsion layer come into contact with it. Thesilver precipitating agent may comprise either physical developmentnuclei or a chemical precipitant for silver ions.

Suitable silver precipitating agents for use in the silver precipitatinglayer for forming the argental image include sulfides, selenides,polysulfides, polyselenides, thiourea, mercaptans, stannous halides,heavy metals and heavy metal salts, and fogged silver halide. Heavymetal sultides such as lead, silver, zinc, antimony, cadmium and bismuthsulfides are useful, particularly the sulfides of lead and Zinc alone orin admixture, or complex salts of these with thioacetamide,dithio-oxamide, or dithio-biuret. The heavy metals include silver, gold,platinum, palladium and mercury preferably in the colloidal form. Thenoble metals are particularly efiicacious.

The silver precipitating agents may be applied directly to a supportsuch as paper, or to suitably subbed cellulose derivative supports andsynthetic polymer supports from solutions or dispersions of the silverprecipitating agents in a colloid vehicle such as gelatin. The colloidvehicle of the silver precipitating layer is necessarily insoluble inthe solution used for removing the carboxylated cellulose derivativeemulsion layer in the final stage of the process. If gelatin is used, itshould be hardened. Hydrophilic cellulose esters and synthetic polymersare useful as a vehicle in the silver precipitating layer insofar asthey meet the requirement of having a solubility appreciably differentfrom that of the colloid vehicle of the emulsion layer.

The silver halide component of the mentioned emulsions is not especiallycritical and can include various silver halides and mixtures of silverhalides such as silver bromoiodide, silver chloride, silver chlorobromide or silver bromide optically sensitized in the usual manner. Theemulsions may be developing-out emulsions designed for development tonegative images in which case the image obtained in the silverprecipitating layer is a positive with respect to the original subject.If desired, the emulsion can be of the direct positive type with theresult that the silver image developed in the emulsion is a positive andthe image in the silver precipitating layer a negative in respect to theoriginal subject. The procedures of Leermakers U.S. Patent 2,184,013 andKendall et al. U.S. Patent 2,541,472 are useful in conferring the directpositive characteristics to the emulsions.

As mentioned, the colloid vehicle of the silver halide emulsion appliedto the silver precipitating layer is an alkali-soluble acid-insolublecarboxylated cellulose derivative such as a dibasic acid half-ester of acellulose ethyl ether; however, a portion of the colloid vehicle may besome other water-soluble organic colloid such as unhardened gelatin inminor quantity and of a kind such that the removal of the emulsion layeris not adversely affected in the later stages of the process.

Representative carboxylated cellulose derivatives are the alkali-solubleacid-insoluble dibasic acid esters of the cellulose ethyl ethersincluding the phthalic, succinic, and maleic acid esters of ethylcelluloses and their ammonium, alkali metal and amine salts, the estersbeing made from cellulose ethyl ethers having an alkoxy content of atleast 42 percent and the esters having a dicarboxylic acid radicalcontent of at least 5 percent and preferably at least 20 percent.

The ethyl cellulose phthalates made from cellulose ethyl ethers havingat least 42 percent ethoxyl and containing at least 5 and preferablyabout 20 percent phthalyl are particularly efficacious for use in theemulsion layer of the sensitive elements of our invention. Thus asatisfactory cellulose ether phthalate can be made by the esterificationof a cellulose ethyl ether containing 42% ethoxyl until about 5 tophthalation has taken place. A preferred cellulose ether phthalate isthus made from a cellulose ethyl ether containing 45% ethoxyl, the finalester containing about 24% phthalyl. The viscosity of this ester wasabout 3 to 6 cps. in a 3% solution containing 70% ethyl alcohol,isopropyl alcohol and 10% butanol. The ethyl cellulose phthalatesemployed may vary also as to viscosity. We have found that in the caseof low viscosity esters, such as those whose salts have a viscosity ofless than 10 cps. in 4 percent solution in water, it may be desirable toincorporate some plasticizer, such as triacetin or polyethyleneglycol inthe ethyl cellulose phthalate composition.

The preparation and properties of these ether phthalates and methods forpreparing emulsions containing them, suitable for application over thesilver precipitating layer of our sensitive elements is described morefully in the Talbot and McCleary U.S. Patent 2,725,293, granted November29, 1955. In addition to the peptizing agents disclosed in thelast-mentioned invention for preparing the cellulose ether phthalateemulsions, gelatin is equally useful as shown in the exampleshereinafter. Malm et al. U.S. Patent 2,718,667 and Hiatt et al. U.S.patent application Serial No. 272,697, filed February 20, 1952, may alsobe referred to for a description and synthesis of useful cellulose etherphthalates.

The alkali-soluble acid-insoluble dibasic acid esters of celluloseacetate such as various cellulose acetate phthalates are likewise usefulas the emulsion vehicle of the invention. A typical cellulose acetatephthalate contains 34% phthalyl and 19% acetyl. These esters can be madeby methods known in the art or as shown in the above Hiatt et al.invention. Similarly, cellulose phthalate containing about 50% phthalylcan be used as the major part of the emulsion vehicle.

What we claim is:

1. A method of forming a photographic image which comprises exposing toa subject an element including a support, a silver precipitating stratumon the support, and adhered to said stratum a light-sensitive emulsionlayer containing silver halide uniformly dispersed in a member of theclass consisting of an alkali-soluble acid-insoluble dibasic acid esterof a cellulose ethyl ether and an alkalisoluble acid-insoluble dibasicacid ester of a cellulose acetate, developing the latent image in theemulsion layer with an alkaline silver halide developing solutioncontaining a quaternary ammonium salt having a linear chain of at least7 atoms attached to a quaternary nitrogen atom, a hydroquinone, sulfite,a silver halide solvent, potassium chloride and a member of the classconsisting of a monoalkyl-paminophenol silver halide developing agentand a 3-pyrazolidone silver halide developing agent, to form a silverimage and an imagewise distribution of a soluble silver complex in theemulsion layer, allowing a portion of said silver complex to diffuseimagewise to said silver precipitating stratum and the silver of saidportion of silver complex to be precipitated in said stratum, andremoving the emulsion layer from said stratum.

2. A method of forming a photographic image which comprises exposing toa subject an element including a support, a silver precipitating stratumon the support, and adhered to said stratum a light-sensitive emulsionlayer containing silver halide uniformly dispersed in an alkalisolubleacid-insoluble cellulose ethyl ether phthalate, developing the latentimage in the emulsion layer with an alkaline silver halide developingsolution containing a quaternary ammonium salt having a linear chain ofat least 7 atoms attached to a quaternary nitrogen atom, hydroquinone,sulfite, a silver halide solvent, potassium chloride and1-phenyl-3-pyrazolidone, to form a silver image and an imagewisedistribution of a soluble silver complex in the emulsion layer, allowinga portion of said silver complex to diffuse imagewise to said silverprecipitating stratum and the silver of said portion of silver complexto be precipitated in said stratum, and removing the emulsion layer fromsaid stratum.

3. A method of forming a photographic image which comprises exposing toa subject an element including a support, a silver precipitating stratumon the support, and adhered to said stratum a light-sensitive emulsionlayer containing silver halide uniformly dispersed in an alkalisolubleacid-insoluble cellulose ethyl ether phthalate, developing the latentimage in the emulsion layer with an alkaline silver halide developingsolution containing trisodium phosphate, a quaternary ammonium salthaving a linear chain of at least 7 atoms attached to a quaternarynitrogen atom, hydroquinone, a silver halide solvent, potassium chlorideand 1-phenyl-3-pyrazolidone, to form a silver image and an imagewisedistribution of a soluble silver complex in the emulsion layer, allowinga portion of said silver complex to diffuse imagewise to said silverprecipitating stratum and the silver of said portion of silver complexto be precipitated in said stratum, and removing the emulsion layer fromsaid stratum.

References Cited in the file of this patent UNITED STATES PATENTS2,685,514 Haist Aug. 3, 1954 2,704,721 Land Mar. 22, 1955 2,725,293Talbot et al. Nov. 29, 1955 2,855,299 Rogers Oct. 7, 1958

1. A METHOD OF FORMING A PHOPTOGRAPHIC IMAGE WHICH COMPRISES EXPOSING TOA SUBJECT AN ELEMENT INCLUDING AA SUPPORT, A SILVER PRECIPITATINGSTRATUM ON THE SUPPORT, AND ADHERED TO SAID STRATUM A LIGHT-SENSITIVEEMULSION LAYER CONTAINING SILVER HALIDE UNIFORMLY DISPERSED IN A MEMBEROF THE CLASS CONSISITNG OF AN ALKALI-SOLUBLE ACID-INSOLUBLE DIBASIC ACIDESTER OF A CELLULOSE ETHYL ETHER AND AN ALKALISOLUBLE ACID-INSOLUBLEDIBASIC ACID ESTER OF A CELLULOSE ACETATE, DEVELOPING THE LATENT IMAGEIN THE EMULSION LAYER WITH AN ALKALINE SILVER HALIDE DEVELOPING SOLUTIONCONTAINING A QUATERNARY AMMONIUM SALT HAVING A LINEAR CHAIN OF AT LEAST7 ATOMS ATTACHED TO A QUATERNARY NITROGEN ATOM, A HYDRO-E QUINONE,SULFITE, A SILVER HALIDE SOLVENT, POTASSIUM CHLORIDE AND A MEMBER OF THECLASS CONSISTING OF A MONOALKYL-P AMINOPHENOL SILVER HALIDE DEVELOPINGAGENT TO FORM A SILVER OLIDONE SILVER HALIDE DEVELOPING AGENT, TO FORM ASILVER IMAGE AND AN IMAGEWISE DISTRIBUTION AGENT, TO FORM A SILVERCOMPLEX IN THE EMULSION LAYER, ALLOWING A PORTION OF SAID SILVER COMPLEXTO DIFFUSE IMAGEWISE TO SAID SILVER PRECIPI-PLEX TO BE PRECIPITATED INSAID STRATUM, AND REMOVING THE EMULSION LAYER FROM SAID STRATUM.